1. Field of the Invention
The present invention relates to a printer and, more particularly, to a printer which performs printing by supplying continuous paper held by a holding portion to a printing section, and a method of supplying continuous paper to a printing portion.
2. Description of the Related Art
Generally, in a printer, the paper convey speed is determined at a predetermined value corresponding to the printing timing of a line printing head so that the dots are printed by the line printing head to have a predetermined gap between them.
When a line printing head, e.g., a line thermal head, is used, in order to convey the paper at a paper convey speed corresponding to the printing timing, the peripheral speed of each platen roller placed to oppose the line thermal head and a feed roller that supplies paper to a portion between the thermal head and the platen roller is controlled to coincide with the paper convey speed.
For example, in a color printer in which four line thermal heads are sequentially arranged along a paper convey path to perform color printing on the paper by using yellow, magenta, cyan, and black ink ribbons, respectively, the printing errors of the respective line thermal heads appear as color misregistration. Therefore, the peripheral speeds of the four platen rollers respectively placed to oppose the four line thermal heads must be controlled at a higher precision. For this purpose, the peripheral speeds of all the platen rollers, and of a feed roller are controlled at a high precision so that they coincide with the paper convey speed corresponding to the printing timings.
However, when continuous paper is used, the continuous paper is generally rolled, and the paper is withdrawn from the roll and supplied to the thermal heads. In the initial printing stage where the roll diameter is large, the roll portion of the continuous paper has a considerable weight, which causes a starting resistance at the start of the paper convey operation. Thus, a large tension acts on the paper withdrawn from the roll portion. This tension largely varies depending on the roll diameter and the like. A variation in tension acting on the paper causes a variation in printing timing, leading to a disorder in printing.
Furthermore, in the color printer, the shapes and sizes of a plurality of platen rollers have errors due to the limitation in parts precision. It is, therefore, difficult to make the peripheral speeds of all the platen rollers to completely coincide with each other. Accordingly, during conveyance of the paper by these platen rollers, the paper between the platen rollers (paper in the vicinity of a printing head) becomes loose, or an excessive tension acts on the paper to make it slip on a platen, causing disorder in conveyance. A disorder in paper conveyance causes a disorder in printing, e.g., an erroneous printing timing, leading to a printing error such as color misregistration.